The invention relates to a method and apparatus for applying molten size to a plurality of textile strands.
In the process .[.if.]. .Iadd.of .Iaddend.textile sizing, material usually called "size" or "sizing," most commonly in the form of an aqueous solution, is applied to individual textile warp yarn threads or strands to protect them from the physical abuse of the weaving operation. This type of sizing is not to be confused with the operation of applying "sizing" to a finished textile fabric to stiffen it, or add weight, or for other reasons of modifying finished character. In the case of individual warp threads which are treated with a size application before weaving to make them more resistant to the abrasive action of the loom, further purposes are to reduce the hairiness of the strands and thereby to eliminate their tendency to cling together because of such hairiness, to reduce shedding of fibers from the strands because of the abrasive wear on the yarn by mechanical devices during processing, and to reduce the rolling that entangles together adjacent unsized yarns. All of these factors can act to cause thread breakage, machine stoppage, and defects in the finished goods.
Most warp sizing machines in use today, generally termed slashers, apply size to individual warp strands by moving these strands through an aqueous bath of sizing material so that the sizing agent penetrates and adheres to the warp yarn strands. Simultaneous with the wetting of the yarn by size (usually by immersion) is a mechanical squeezing action that accomplishes a quetsching operation when the warp threads pass through the nip of the compressive rollers, usually one being of steel and the other of rubber-covered construction. The rolls also serve to remove excess size. Thereafter, the sized yarns are passed around the heated surface of several drying cylinders that accelerate the evaporation of moisture from the yarn. Thence the size yarn passes to a take-up mechanism to properly package it for the next stage of the manufacturing process.
These warp sizing machines are expensive. They are complex, with a large number of processing variables that are difficult to control satisfactorily. If uncontrolled, these variables can destroy uniformity and reduce the quality of the sized warp yarns and subsequently the woven product. Typical of the apparatus of aqueous warp sizing in the prior art are the U.S. Pat. Nos. to Bouvet 2,478,230, Still, 2,565,407, and Baltzer, 3,247,568. The Still patent features a grooved guide roller bearing a passing resemblance to the grooved applicator roller of the present invention, but differing from it drastically in function, location, groove shape, temperature, and utility in a melt-sizing system.
The system of applying a size dissolved in water to a yarn and depositing it by evaporating off the water is the most commonly practiced sizing method used by the textile industry today. Many less practical and effective ways have been suggested but they have not proved practical for general manufacturing processes. Spraying instead of passing the warp threads through a bath has been suggested. Generally, the suggested modified methods for sizing textile warp yarns all have in common the basic fact that they involve applying the size material from an aqueous or other solvent system, and that the solvent must afterwards be removed, thereby retaining the expense and large space and equipment requirements of the conventional sizing operation. The present invention proposes a method and apparatus have the capacity for applying a polymeric melt size to yarn by a solvent-free method and has as a result the potential of greatly reducing the operational expense and space previously required in conventional sizing operations.
.[.An alternative to aqueous sizing is disclosed in the patent of Kuroda, U.S. Pat. No. 3,466,717. Kuroda describes a melt sizing method and apparatus, but this system is expressly restricted to application of sizing compounds in which wax predominates. The fact that the major component of the size is wax assigns certain inherent characteristics to the size. One of these is a relatively low melt viscosity. Molten waxes are comparable to molten paraffin in viscosity. Castor wax, the "hardened castor oil" of Kuroda, has a viscosity of 9.5 centipoises at 300.degree. F., compared to the 1000- 2000 centipose viscosities of the polymeric sizes for which the present process and apparatus are designed. Even the inclusion of a minor proportion of poly-2-ethylhexyl acrylate in prior art size compounds tried merely to improve the film-forming and thickness characteristics of the melts by addition of a thickener. If the melt viscosity is not relatively low, probably comparable to that of conventional aqueous solutions of sizes, wax-based melt sizes will not, it is believed, process effectively in the applicator chamber of Kuroda. It will be seen, therefore, that the Kuroda apparatus and method very strongly resemble the conventional aqueous sizing system..].